Solvent extraction, solvent dewaxing and hydrotreating a lube oil



nited States Patent 3,403 092 SOLVENT EXTRACTION, SOLVENT DEWAXIN G ANDHYDROTREATING A LUBE OIL Maurice K. Rausch, Homewood, Ill., assignor toSinclair Research, Inc., New York, N.Y., a corporation of Delaware NoDrawing. Filed Apr. 14, 1965, Ser. No. 447,955

6 Claims. (Cl. 208-36) ABSTRACT OF THE DISCLOSURE Oxidation inhibitorsusceptibility of distillate mineral lubricating oils is enhanced by thesteps of treating a distillate lubricating oil fraction by solventextraction to remove aromatic constituents, solvent dewaxing theraflinate to remove waxy components, and then hydrotreating the dewaxedmaterial over a nickel-molybdenumactivated alumina catalyst at about 550to 775 F. and about 800 to 5000 p.s.i.g. hydrogen partial pressure, andpreferably at about 625 to 725 F. and about 0.5 to 2 WHSV. The catalystcan be sulfided. Oils obtained by this process have great inhibitorsusceptibility and as a result can be protected against oxidationbreakdown for a long period of time. Conventional antioxidants, such assulfur compounds, phosphorous compounds, and amine and phenolderivatives, are effective in the oils.

This invention relates to the treatment of mineral lubricating oils inorder to improve their additive susceptibility characteristics. Morespecifically, this invention relates to the treatment of a distillatemineral lubricating oil by a series of processing steps including solvent extraction, solvent dewaxing and hydrotreating with anickel-molybdenum catalyst in order to obtain a lubricating oil ofimproved oxidation inhibitor susceptibility.

It is well known that mineral oil based liquid lubricants suffer fromthe effect of oxidation when used in high temperature applications. Theoxidation products may include organic acids and complex condensationand polymerization products which are undesirable. In order to inhibitoxidation, it is customary to add an oxidation inhibitor to alubricating oil. Small amounts of inhibitor are normally effective inpreventing oxidation for a limited period of time. However, oxidationinhibition for the longer periods of time required in normal use isoften unobtainable by merely adding larger quantities of inhibitor. Afrequent experience is that inhibitors when present in large amountswill not give inhibition for a significantly longer period than theygive when used in much smaller amounts. In other words, thesusceptibility of the oil to an inhibitor is normally relatively low andthe oil is not too responsive to larger amounts of inhibitor.

It is an object of this invention to provide an oil of improvedoxidation inhibitor susceptibility in order that long term oxidationresistance can be obtained by simply adding an increased amount ofoxidation inhibitor. It is a further object to provide a novelcombination of oil and oxidation inhibitor having improved long termoxidation resistance.

It has been found that high oxidation inhibitor susceptibility can beobtained by solvent extraction of a distillate lubricating oil fractionto remove aromatic 'ice constituents, solvent dewaxing the resultingmaterial to remove waxy components and yield an oil of low pour point,and then hydrotreating the product over a nickelmolybdenum-activatedalumina catalyst. An oil obtained according to this process has a greatinhibitor susceptibility and as a result can be protected againstbreakdown due to oxidation for a long period of time.

In refining of mineral oils a reduced crude is normally fractionated toyield a distillate oil, e.g. a light lube oil having a viscosity in therange of about 60 to Saybolt seconds at 100 F., a medium lube oil havinga viscosity in the range of SAE 10 to SAE 20 and a heavy lube oil havinga viscosity in the range of SAE 40 to SAE 60. Any of these fractions orother distillate fractions if desired may be used in the process of thisinvention.

The first step of my method is the solvent extraction of a desired lubefraction to remove aromatic constituents. Solvent extraction is aconventional step and may be accomplished according to any one of anumber of well known methods. The solvents used in this steppreferentially dissolve aromatic type hydrocarbons, have much lesspreference for naphthene hydrocarbons and little or no solubility forparaffinic hydrocarbons. The solvent selected for aromatics is normallyonly partially miscible with the oil undergoing treatment so that twophases are formed, a raflinate phase containing a refined oil of reducedaromatic content and an extract phase containing the selective solventand aromatic hydrocarbons. Suitable selective solvents are furfural,phenols, liquid S0 nitrobenzene, dimethyl formamide and the like. Thevolumet. ric ratio of solvent to oil may vary from about 1 to 2:1. Theextraction temperature may vary from about 100 to 200 F. with thepreferred temperature being about to F.

In the second step, the raflinate from the solvent extraction is solventdewaxed in order to remove waxy components and yield an oil of low pourpoint. In a typical dewaxing operation, a preferential solvent for theliquid oil constituents is used to separate the Waxy from the non-waxycomponents. Typical dewaxing solvents contain a mixture of an aromatichydrocarbon containing from 6 to 8 carbon atoms per molecule, e.g.benzene, toluene, or mixtures thereof; and an aliphatic or alkyl ketonehaving from 3 to 8 carbon atoms per molecule, such as acetone, methylethyl ketone, methyl propyl ketone, methyl isobutyl ketone or mixturesthereof. For example, a suitable dewaxing solvent comprises a mixture ofabout 40 to 60 volume percent of an aromatic hydrocarbon such as tolueneand 40 to 60 volume percent of an aliphatic ketone such as methyl ethylketone. Useful solvent to oil ratios may vary from about 0.5:1 to 2:1.The dewaxing operation is carried out at a temperature sulficiently lowenough to obtain the desired amount of wax removal. Normally the filtertemperature will range from about 30 F. to +20 F. with the preferredrange being from about -20 F. to +10 F.

After the dewaxing operation it may be desirable to adjust productviscosity and boiling range by a distillation step. At this point aclose distillation cut can be made on a smaller volume of oil whichcontains less wax and aromatics.

The next step in my process is hydrotreating using a nickel-molybdenaactivated alumina catalyst. The temperature used in the hydrotreatingmay be from about 550 to 775 F. with the preferred range being about 625to about 725 F. The oil to be hydrogenated is contacted with addedmolecular hydrogen in the presence of the solid nickel-molybdenacatalyst. Any suitable hydrogenation reactor may be employed. Forexample hydrogen and oil may be contacted with either a stationary ormoving catalyst bed. The hydrogen rate may often vary from about 300 toabout 5000 s.c.f./b. (standard cubic feet per barrel of oil), with thepreferred rate being from about 500 to about 2000 s.c.f./ b. Thehydrogen partial pressure ranges from about 800 to 5000 p.s.i.g. withthe preferred range being from about 1000 to 2500 p.s.i.g. The spacevelocity should normally range from about 0.25 to 4 WHSV (weight hourlyspace velocity, pounds of oil per pound of catalyst per hour) andpreferably from about 0.5 to 2 WHSV.

The catalyst used in the hydrotreating step of this process is acalcined or activated catalyst comprising catalytic amounts of nickeland molybdenum on activated alumina. The catalyst may contain about 1 to30 weight percent molybdenum and about 1 to weight percent nickel. Thepreferred composition is about 8 to weight percent molybdenum and 2 to10 weight percent nickel. The catalyst may be formed by impregnatingactivated alumina with nickel and molybdenum compounds in an aqueousmedium. The aqueous medium may be a solution or a slurry containingeither water insoluble compounds or water soluble compounds such asnickel acetate, nickel nitrate, nickel chloride, nickel perchlorate,molybdenum bromide, molybdenum trioxide, ammonium para molybdate etc.After deposition of the molybdenum and nickel compounds, the catalystcan be dried and calcined or activated, e.g. at a temperature in therange of about 600 to 1300 F. or higher.

A preferred form of the catalyst consists of an activated alumina basehaving minor, catalytically effective amounts of molybdenum and nickeldeposited thereon by double impregnation. The total amount ofcatalytically active components in the doubly impregnated catalyst canvary considerably while being sufficient to afford a substantialcatalytic effect. The finely divided alumina base which is doublyimpregnated may first be impregnated by adding nickel and molybdenumcomponents in an aqueous medium. The impregnated material is calcinedfor instance at temperatures of about 600 to 1300 F. or more. Aftercalcination the catalyst is again impregnated with nickel andmolybdenum, dried and calcined at about 600 to 1300 F. or more.

The catalyst of the invention is particularly active when the activatingmetals, for instance in the oxide form, are converted to the sulfides.To convert the metal oxides to the sulfides, the calcined aluminacatalyst may be sulfided by passing hydrogen sulfide, either pure ordiluted with another gas such as hydrogen, over the catalyst attemperatures usually below about 800 F., preferably about 300 to 600 F.for a time sufficient to convert a significant portion of the oxides ofthe metal components to their respective sulfides.

Treatment of an oil according to the foregoing process yields a lube oilhaving generally improved antioxidant additive susceptibility. Thus anyconventional antioxidant will normally be more effective in relativelylarge quantities in oils treated according to this invention. Typical ofthe antioxidants which have increased etfectiveness due to thisinvention are sulfur compounds, phosphorous compounds and amine andphenol derivatives. Examples of sulfur compounds are sulfurized fattyoils and olefins, sulfurized terpenes, aromatic sulfides such asdibenzyl sulfides and phenol sulfides such as dibutyl phenol sulfides.Suitable phosphorous compounds are organic phosphites such as triphenylor tributyl phosphite and alkyl phosphates. Typical phosphorous andsulfur compounds are zinc dithiophosphate. Typical amines arediphenylamine and diamincs such as tetramethyl diaminodiphenylmethane.Phenol derivatives which may be used advantageously are for examplebeta-naphthol pyrogallol, alizarin and the oil soluble alkylatedphenols. The oil-soluble, alkylated phenols are preferred and ordinarilycontain 1 to 5 alkyl groups each of 1 to 6 or more carbon atoms.Particularly preferred alkylated phenols are the alkylated cresols suchas dibutyl p-cresol. In general, antioxidants provided the oils of thepresent invention will be present in amounts of about 0.1 to 5% byweight, preferably about 0.7 to 3%.

The process of this invention and improved properties of oils treatedaccording to the invention are illustrated by the following example.

Example A neutral lube distillate obtained as a side stream from thevacuum distillation of a Mid-Continent based crude was employed as thestarting material. The neutral lube distillate tested as follows:

Gravity API 30.3 Flash point, F. 385 Viscosity (cs.) at 210 F. 3.655Aniline point, C. 90.2

This raw, vacuum sidestream was solvent extracted using phenol in aphenol-to-oil ratio of 1.63 to 1. A 64.3% yield of waxy raffinate wasobtained and the waxy raffinate was solvent dewaxed using a 6040 mixtureof methyl ethyl ketone and toluene as the solvent for selectivecrystallization of the paraffinic components. The solventto-oil dilutionused in the solvent dewaxing was 1.45 to l. the oil solvent mixture wasfiltered at l5 F. to yield 78.7% dewaxed raffinate. The dewaxedrafiinate was then fractionated to yield a 55.2% oil fraction of desiredviscosity and boiling range. This material is identified as Oil A inTable I. Oil A was then hydrogen-treated under the following processconditions using two alternate catalyst types. These catalyst types were(1) cobalt-molybdenum on activated alumina containing 3% C00 and 10% M00and (2) nickel-molybdenum on activated alumina containing 4% NiO and 16%M00 In the case of both catalysts, the catalytic metal oxides wereconverted to their sulfide form by treatment with H S at 350 F. at arate of 6 standard cubic feet per hour per catalyst charge of 150 grams.

Hydrogen partial pressure, p.s.i.g 1500 Temperature, F. 650 Spacevelocity, WHSV 1.0

Hydrogen rate, s.c.f./b. 1500 The products were put through a steamstripping operation using a steam rate of 10 lbs./bbl. to remove any hy-TABLE I Oil A. Oil B Oil 0 Gravity, API 32. 4 32. 7 33.0 Flash point, F415 405 395 ire, 460 445 465 Viscosity, (3. at F. 25. 98 25. 08 24. 73Viscosity, cs. at; 210 F. 4. 539 4. 462 4. 447 Pour point, F +10 +5 +10Color, ASTM L1. 5 L0. 5 L0. 5 Specific dispersion 105. 5 104. 2 102. 8Refractive index at 20 0.. 1. 4740 1. 4737 1. 4728 Iodine number 8. 6 3.4 2.7

These oils were then formulated with an oxidation inhibitor. Thespecific oxidation inhibitor used was dibutylparacresol (DBPC) and twoadditive levels of this oxidation inhibitor were used with each oil.These oils were then evaluated for oxidation resistance in the TurbineOil Stability Test (TOST), ASTM D-943. Oxidation life 2. The method ofclaim 1 wherein the hydrotreating was determined as hours running timeto 2.0 acid numis carried out at a temperature of about 625 to 725 F.ber. Data on acid number and ASTM color throughout and a weight hourlyspace velocity of about 0.5 to 2 the oxidation runs are presented below:WHSV.

Oil B-Hydrogcnated over cobalt-moly catalyst Oil C-Hydrogeuated overnickel-moly catalyst containingcontaining- Hours TOST time 0.4% DBPC1.0% DBPC 0.4% DBPO 1.0% DBPO Acid No. Color Acid No. Color Acid No.Color Acid No. Color 1,000 0.08 L2.0 0.08 Lao 0. 05 2.5 0. 07 L2.[] 1,344.. t 0. 08 L3. L2. 0

3533:: "a: TOST induction period (hours) 2, 050

These data illustrate the greatly enhanced susceptibility 3. The processof claim 2 wherein the catalyst conto oxidation inhibitors of Oil Cwhich was hydrogenated tains from about 2 to 10 weight percent nickeland about over the nickel-moly type catalyst. As would be expected, 8 toweight percent molybdenum. this superiority is especially evidenced atthe higher con- 4. The process of claim 3 wherein the nickel andcentration level of oxidation inhibitor. molybdenum are present in theform of sulfides.

It is claimed: 5. A lubricating composition consisting essentially of 1.A method of producing a mineral oil of lubricating a mineral oil oflubricating viscosity prepared according viscosity having enhancedsusceptibility to oxidation into the method of claim 1 and small amountsof an oilhibitors consisting essentially of subjecting a distillate balkylated phenol as an antioxidant,

mineral lubricating oil fraction to solvent extraction at Thecomposition f claim 5 h i h oxidation a temperature of about 100 to Wltha solvent inhibitor is dibutyl para-cresol in an amount of aboutselective for aromatic hydrocarbons, and at a solvent to to oilvolumetric ratio of about 1:1 to 2:1 to produce a raffinate of reducedaromatic content, solvent dewaxing References Cited said raffinate witha solvent consisting essentially of a UNITED STATES PATENTS mixture ofan aromatic hydrocarbon of 6 to 8 carbon 1,945,521 2/1934 Downing et a1.atoms and an alkyl ketone of 3 to 8 carbon atoms at a 3 011 972 12/1961Watson et a1 208 264 solvent to oil volumetric ratio of 0.5:1 to 2:1 anda tem- 3252887 5/1966 Rizzuti 2O8 264 perature of from about --30 F. to20 F. to yield a sol- 175 6/1966 Kozlowsiqfg'g'l 208 264 vent dewaxedoil, and hydrotreating said dewaxed oil in the presence of anickel-molybdenum-activated alumina catalyst at a temperature of fromabout 550 to 775 F. D ELBERT GANTZ Pllmary Exammer and a hydrogenpartial pressure of about 800 to 5000 S, P, JONES, Assistant E aminp.s.i.g.

